Tonometer



M. J. ALLEN June 9, 1964 MM NSE L m.. 8 2 4 O J 4 4 [.1 l O H 2 d M 1 a H 6 i- 6 H m w m w, HW l H 2 n MO l r 0 w 6 I I. 8 w 2 4 FIG. 2.

FIG.

' ATTORNEY United States Patent 3,136,152 TONOMETER Merrill .1. Allen, Bloomington, Ind, assignor to Raymond 0.. Gulden, Philadelphia, Pa. Filed June 20, 1963, Ser. No. 289,263 2 Qlaims. (Cl. 73-450) This invention relates to tonometers of the type used for measuring ocular tension.

While, as will become apparent, the invention is more generally applicable to tonometers, it may be conveniently described as applied to the type of tonometer illustrated and described in the patent to Raymond 01 Gulden, No. 3,062,042, dated November 6, 1962. From the standpoint of general manipulation and operation the tonometer of that patent is typical. As the tonometer is lowered on the eye of a patient it is supported by the fingers through a bracket within which there may vertically slide the main body of the tonometer which terminates at its lower end in a concave foot shaped to fit the eye. Within this body there is arranged to slide a plunger the lower end of which projects, as the tonometer approaches the eye, below the lower concave surface of the foot. Typically the protrusion has been to the extent of three millimeters. In the lowering operation the plunger first engages the eye and then the foot is lowered to its rest position and the supporting bracket permitted to move further downwardly. The effective tension is then read on a scale by means of a pointer which actually responds to the extent of movement of the plunger below the surface of the foot under the action of a standard Weight applied to the plunger.

The operational movements thus involved have a disadvantage which may be particularly serious in the case of an inexperienced operator of the instrument. While a plunger has smooth edges, the fact that it contacts the eye first and is forced upwardly into the foot means that, by reason of its relatively small cross-sectional area, it indents the eye so that any accidental lateral movement relative to the eye may possibly produce damage. Such lateral relative movement may be occasioned either by the operator in attempting to achieve centering or by inadvertent movements of the eye by the patient and these may damage corneal epithelium during corneal tonometry or may cause a wrinkling of the conjunctiva under the foot plate during scleral tonometry. Under the latter conditions exact self-centering of the tonometer foot plate on the surface of the eye is unlikely. Enough abrasion may occur to produce damage or, at least, irritation.

In accordance with the invention, the plunger is held retracted within the foot until the full weight of the tonometer assembly is borne by the eye. The area of the foot presented to the eye is very much larger than that presented by the plunger and the contact is thus smooth and relative movement may occur without damage or irritation. As the approach to the eye is made, the loosely held instrument will center itself readily. There after as the bracket is still further lowered the plunger will move into contact with the eye but not readily subject to lateral movements. As will become apparent hereafter, the weight of the tonometer and the weight applied to the plunger are unaltered as compared with standard tonometers, so that no new technique of operation or interpretation is required.

The general object of this invention relates to the achievement of the foregoing, and this and other objects relating to details will become apparent from the following description, read in conjunction with the accompanying drawing, in which:

FIGURE 1 is a front elevation of the improved tonometer; and

FIGURE 2 is a section taken on the broken surface shown at 22 in FIGURE 1.

The tonometer illustrated comprises the frame 2 having base 4 and a pair of cross struts 6 and 8 secured to the main portion of the frame by suitable spacers and screws. Between them these struts provide a space for the rocking of the anvil 10 which has a shaft engaged in jewel bearings indicated at 12. As is usual, the anvil 10 has secured thereto a pointer 14, which has a curved upper end as indicated at 16 extending upwardly and over a curved scale member 18, of light material such as aluminum, secured to the upper ends of the arms of the frame 2. The surface of the scale member 18 adjacent to which the pointer moves is in the form of a segment of a torus having the axis of the anvil as its center. The pointer 14 has its upper end 16 slightly spaced from the scale member which carries the conventional markings 20, which are extended about the toroidal surface of the scale member. Stop pins 21 limit the range of movement of the pointer relative to the scale. As will be evident the construction just described makes possible the reading of the position of the pointer against the scale through a large angle of view ranging, more or less, through Thus, the tonometer is convenient to use since the user does not have to bring his eye level to that of the scale for proper reading.

The cylinder 22 is externally threaded at its upper end to receive an adjusting nut 24 which is arranged to be held in adjusted position by a set screw 26. The cross member 4 of the frame 2 is secured to this nut by swaging or in other fashion, and zero adjustment is thus provided as is conventional.

The cylinder 22 is provided with the usual downwardly concave foot 28 to conform with the eye.

The plunger 36 is mounted in the bore of the cylinder 22 and is threaded at its upper end as shown at 32 to receive the usual weight 34 which, in its lowermost position in engagement withthe upper end of the cylinder, provides the standard three millimeter protrusion of the lower end 38 of the plunger 39 from the foot 28. This weight, as usual, is provided with a hub portion which serves for the reception of additional weights. The upper projecting portion 36 of the plunger is adapted to engage the pivoted anvil 19.

For support of the elements described there is the bracket 40 which is formed of sheet material and comprises the cross member 42 from which there projects downwardly the portion 44 having a horizontally directed end 46. The cross member 42 and the end 46 have openings loosely embracing the cylinder 22 to provide free relative axial motion when the tonometer is in use.

The upwardly extending arms of the bracket 40 are provided with sockets as indicated at 48 for the reception of the finger and thumb of the user. By reason of the provision of the sockets, a release of pressure provides for quite free pivoting of the bracket and the rest of the assembly about a horizontal axis. The parts are so constructed that the center of gravity of the assembly of frame 2, cylinder 22 and their associated parts is well below a transversed line through the sockets 48 and so located that when the sockets are freely pivoted on the fingers of the user the axis of the plunger and cylinder is very nearly vertical. The existence of this condition is particularly aided by constructing the frame 2, struts 6 and 8 and scale member 18 of light material such as aluminum, the remaining dependent parts being considerably heavier due to their formation from stainless steel.

The prevention of rise of tears by capillary action is elfected by the provision of a groove in the interior of the cylinder 22 having free drainage openings to the exterior. This is accomplished by the drilling of one or more holes through the cylinder 22 just above the foot saaegsa E 28. A desirable arrangement is one in which three holes 50 are radially drilled at 120 spacing from each other, each hole having a diameter slightly larger than the diameter of the axial bore of the cylinder. The result of the intersection of these holes, then, is the provision, in effect, of an annular groove which throughthe holes 50 has drainage outlets to the exterior of the cylinder. As will be evident, tears may rise by capillary action through a quite short distance from the lower surface of the foot 23 to the location of the groove, but this is unobjectionable because of the limited extent of such capillary rise and because the accumulation of solids, if any, may be readily flushed out merely by running water into the holes 50 while imparting oscillatory movements to the plunger.

The foregoing describes matters which are found in said Gulden patent. The matters of the present invention are achieved in a very simple fashion from a mechanical standpoint. The only change from the instrument of said patent is in the provision of a pin or equivalent member 52 secured to the cross-member 42 of the bracket which projects upwardly in a position to engage the lower edge of the weight 34 carried by the plunger 30. The arrangement may be as illustrated, the pin 52 engaging the weight at its periphery.

As will be evident from the figures of the drawing, the length of the pin 52 is such that, when the nut 24 rests on and is supported by the cross member 42, the weight 34 rests on the pin and the lower end 38 of the plunger 38 is held slightly above the concave surface of the foot.

The operation is as follows:

The figures of the drawing show the tonometer with the parts in positions whichare assumed when it is suspended free of the eye by the fingers of the operator entering the sockets 43. As the tonometer is lowered on the eye, the

foot 28 first engages the eye and by reason of its large smooth area presented to the eye it may, by sliding movement, be adjusted to the desired position, the operator making these adjustments gently while sensing through his fingers the existence of contact. Following centering, the operator will then further lower the bracket, and as this occurs the full weight of the suspended assembly is brought on the eye and, by continuing lowering movements, the pin 52 then releases the plunger so that it is lowered to indent the eye as is required for the making of a measurement. Finally the lowering is carried to the extent of completely releasing the weight 34 by further downward movement of the pin so that the indentation takes place .raised the pin 52 first engages the weight 34 to lift the plunger and the plunger is withdrawn above the undersurface of the foot before the foot can be raised. Thus again during removal the possibility that the plunger will move relatively to the eye while indenting it is minimized. Finally, full upward raising of the bracket 40 will pick up the nut 24 to lift the foot from the eye.

As will be seen from the foregoing, there is achieved fully and effectively the prevention of contact of the plunger with the eye except when the foot is resting on the eye. It will be evident that details of the plunger lifting arrangement may be changed without departing from the invention as defined in the following claims.

What is claimed is:

1. A tonometer comprising a member having a lower foot portion, said foot portion having a concave surface adapted to overlie and rest upon the surface of the eye, said member having a vertical bore therein extending upwardly from said concave surface, an elongated weighted plunger in said bore and having a sliding fit therein, said plunger having a lower portion projecting downwardly beyond said concave surface for depressing the surface of the eye, a frame secured to said member and extending upwardly thereof, said frame mounting a scale, and a pointer for movement relative to said scale, said pointer being operatively connected to move in response to movement of said plunger, a support bracket adapted to be supported, by the fingers of a user, for upward movement of the member relative to said bracket and arranged to support and slidably mount said member, and means carried bysaid bracket and engageable with said plunger when said bracket supports said member to withdraw the eye-depressing portion of the plunger above the concave surface of said foot portion.

2. A tonometer according to claim 1 in which the last mentioned means is provided by a pin carried by said bracket and arranged to abut a portion of the plunger.

No references cited. 

1. A TONOMETER COMPRISING A MEMBER HAVING A LOWER FOOT PORTION, SAID FOOT PORTION HAVING A CONCAVE SURFACE ADAPTED TO OVERLIE AND REST UPON THE SURFACE OF THE EYE, SAID MEMBER HAVING A VERTICAL BORE THEREIN EXTENDING UPWARDLY FROM SAID CONCAVE SURFACE, AN ELONGATED WEIGHTED PLUNGER IN SAID BORE AND HAVING A SLIDING FIT THEREIN, SAID PLUNGER HAVING A LOWER PORTION PROJECTING DOWNWARDLY BEYOND SAID CONCAVE SURFACE FOR DEPRESSING THE SURFACE OF THE EYE, A FRAME SECURED TO SAID MEMBER AND EXTENDING UPWARDLY THEREOF, SAID FRAME MOUNTING A SCALE AND A POINTER FOR MOVEMENT RELATIVE TO SAID SCALE, SAID POINTER BEING OPERATIVELY CONNECTED TO MOVE IN RESPONSE TO MOVEMENT OF SAID PLUNGER, A SUPPORT BRACKET ADAPTED TO BE SUPPORTED, BY THE FINGERS OF A USER, FOR UPWARD MOVEMENT OF THE MEMBER RELATIVE TO SAID BRACKET AND ARRANGED TO SUPPORT AND SLIDABLY MOUNT SAID MEMBER, AND MEANS CARRIED BY SAID BRACKET AND ENGAGEABLE WITH SAID PLUNGER WHEN SAID BRACKET SUPPORTS SAID MEMBER TO WITHDRAW THE EYE-DEPRESSING PORTION OF THE PLUNGER ABOVE THE CONCAVE SURFACE OF SAID FOOT PORTION. 